1. Field of the invention
The present invention relates to an improvement in the cooling structure of a watercool engine and, more particularly, to an engine cooling structure in which a water pump causing to flow a cooling water for cooling an engine is located at or near one end portion of a cylinder block and positioned in the direction of the cylinder alignment.
2. Description of Prior Art
A watercool engine generally includes a water pump for causing a water for cooling an engine to flow, which is located at or near one end portion of an engine body in the direction of the cylinder alignment and which causes the cooling water or coolant pumped therefrom to flow from the one end portion of the engine body to a water jacket in the engine body.
Passages through which the cooling water passes include a main coolant passage leading the cooling water from the water pump outlet to the cylinder block and a cylinder head, a radiator circulating passage circulating the cooling water led to the main coolant passage through a radiator core and then leading it to the inlet portion of the water pump, a by-pass passage by-passing the cooling water led to the main coolant passage disposed in the cylinder head from the radiator core and leading it to the inlet portion of the water pump, and a heater circulating passage circulating a portion of the cooling water led to the main coolant passage through an air-conditioning heater and leading it to the inlet portion of the water pump. Among the passages, the by-pass passage and the radiator circulating passage are constructed so as to be opened or closed by a thermostat valve that senses temperatures of the cooling water. This arrangement is disclosed in Japanese Patent Publication No. 29,248/1980.
U.S. Pat. No. 3,636,935 discloses a structure of coolant passages in which a by-pass passage connecting a main coolant passage disposed in the cylinder head to the inlet portion of the water pump and a return passage connecting an air-conditioning heater mounted on the heater circulating passage to the inlet poriton of the water pump are formed each of a long length of a pipe mounted outside the engine body. Accordingly, an early deterioration in pipes is caused to occur due to radiant heat from an exhaust manifold if the pipes are mounted on the side of the exhaust system of an engine. And this arrangement makes a layout of parts around the engine body complicated and difficult so that the assembly of the engine body is rendered laborious. Furthermore, pipes are required to be bent into complex shapes and a resistance to flow in passages becomes high.